It has been demanded that some types of capacitors, solid electrolytic capacitors having low equivalent series resistance and adapted for use with CPUs in personal computers or aluminum electrolytic capacitors employed for smoothing in power circuits, have a small size and a large capacitance.
A solid electrolytic capacitor includes an electrode foil (anode) having a dielectric film disposed on a surface thereof, a solid electrolyte layer made of conductive polymer disposed on the dielectric film, and an cathode layer disposed on the solid electrolyte layer.
FIG. 11 is a schematic cross sectional view of a conventional electrode foil 1 disclosed in Patent Literature 1. The electrode foil 1 includes a substrate 2 made of valve metal foil, a rough layer 3 disposed on the substrate 2, and a dielectric film disposed on the rough layer 3. The substrate 2 and the rough layer 3 serve as a positive electrode of the solid electrolytic capacitor.
The rough layer 3 is formed by vapor deposition and composed of plural fine metallic particles 4 which are joined with one another and extending from the surface of the substrate 2. This structure provides the electrode foil 1 with a large surface area per unit size, accordingly providing the capacitor with a large capacitance.
The dielectric film is formed by anodizing the fine particles 4 in the rough layer 3 and coating the surface of the rough layer 3 with metal oxide.
The capacitor fabricated with the electrode foil 1 may have a leakage current increasing.